Shape changing structures will play an important role in future engineering designs since rigid structures are usually only optimal for a small range of service conditions. Hence, a concept for reliable and energy-efficient morphing structures that possess a large strength to self-weight ratio would be widely applicable. We propose a novel concept for morphing structures that is inspired by the nastic movement of plants. The idea is to connect prismatic cells with tailored pentagonal and/or hexagonal cross sections such that the resulting cellular structure morphs into given target shapes for certain cell pressures. An efficient algorithm for computing equilibrium shapes as well as cross-sectional geometries is presented. The potential of this novel concept is demonstrated by several examples that range from a flagellum like propulsion device to a morphing aircraft wing.

No abstract

No abstract

The Coulomb friction model is frequently used for sheet metal forming simulations. This model incorporates a constant coefficient of friction and does not take the influence of important parameters such as contact pressure or deformation of the sheet material into account. This article presents a more advanced friction model for large-scale forming simulations based on the surface changes on the micro-scale. When two surfaces are in contact, the surface texture of a material changes due to the combination of normal loading and stretching. Consequently, shear stresses between contacting surfaces, caused by the adhesion and ploughing effect between contacting asperities, will change when the surface texture changes. A friction model has been developed which accounts for these microscopic dependencies and its influence on the friction behavior on the macro-scale. The friction model has been validated by means of finite element simulations on the micro-scale and has been implemented in a finite element code to run large scale sheet metal forming simulations. Results showed a realistic distribution of the coefficient of friction depending on the local process conditions.

No abstract